1. Field of the Invention
The present invention relates to regulating circuits, and particularly to a central processing unit (CPU) frequency regulating circuit.
2. Description of Related Art
Conventionally, working frequency of a computer is set by manipulating jumpers or other switches on a motherboard of the computer. The jumpers are changed in accordance with instructions in a user guide of the motherboard so as to change a CPU multiple frequency factor and to control the frequency generation of a frequency generator. This, however, may be troublesome to ordinary consumers since most people are not familiar with such a technique, and thus, although the user may follow the instructions of the user guide, it is still possible and very often that the computer user cannot perform the frequency modification operation correctly.
An incorrect setting of the working frequency may result in damage to the CPU. Therefore to overcome such a problem, some of the computer motherboard manufacturers provide a solution which allows the computer user to set the multiple frequency factor directly on the computer screen, similar to the general setting operation of the computer BIOS.
The conventional way of setting the working frequency is to perform the operation under the condition that the computer is already booted. The setting operation provides frequency information and a frequency switching address signal, which after being decoded, is stored in a storage device. In response to the frequency information, the storage device generates a corresponding multiple frequency factor signal and a frequency selection signal, which are applied to the CPU, and a frequency generator signal and a reset signal are sent from a resetting unit to the CPU and the system chipset to enter a hardware-resetting mode. After the resetting operation, the system chip supplies a reset feedback signal to clear the previous status of the resetting unit which permits the CPU and the system chipset to operate based on the newly selected multiple frequency factor and working frequency. Although this way provides an effective switching operation between different frequencies, it requires additional parts, such as the resetting unit and the storage device. This device and unit may constitute a substantial cost loss to the computer main board manufacturers who usually mass produce computer main boards so that even a tiny increase of the cost for each piece of computer main board would eventually result in a major loss of money for the computer main board manufacturers.
What is needed, therefore, is a CPU frequency regulating circuit for selecting a frequency of the CPU automatically at a low cost.